.TH WQRS 1 "7 January 2009" "WFDB 10.4.12" "WFDB Applications Guide"
.SH NAME
wqrs \- single-channel QRS detector based on length transform
.SH SYNOPSIS
\fBwqrs -r\fR \fIrecord\fR [ \fIoptions\fR ... ]
.SH DESCRIPTION
.PP
\fBwqrs\fR attempts to locate QRS complexes in an ECG signal in the
specified \fIrecord\fR.  The detector algorithm is based on the length
transform.  The output of \fBwqrs\fR is an annotation file (with
annotator name \fBwqrs\fR) in which all detected beats are labelled
normal; the annotation file will also contain optional J-point
annotations if the \fB-j\fR option (see below) is used.
.PP
\fBwqrs\fR can process records containing any number of signals, but
it uses only one signal for QRS detection (signal 0 by default; this
can be changed using the \fB-s\fR option, see below).  \fBwqrs\fR is
optimized for use with adult human ECGs.  For other ECGs, it may be
necessary to experiment with the sampling frequency as recorded in the
input record's header file (see \fBheader\fR(5)), the detector threshold
(which can be set using the \fB-m\fR option), and the time constants
indicated in the source file.
.PP
\fBwqrs\fR optionally uses the WFDB library's \fIsetifreq\fR function
to resample the input signal at 120 or 150 Hz (depending on the mains
frequency, which can be specified using the \fB-p\fR option).  \fBwqrs\fR
performs well using input sampled at a range of rates up to 360 Hz and
possibly higher rates, but it has been designed and tested to work best
on signals sampled at 120 or 150 Hz.
.PP
\fIOptions\fR include:
.TP
\fB-d\fR
Dump the raw and length-transformed input samples in text format on the
standard output, but do not detect or annotate QRS complexes.
.TP
\fB-f\fR \fItime\fR
Begin at the specified \fItime\fR in \fIrecord\fR (default: the beginning of
\fIrecord\fR).
.TP
\fB-h\fR
Print a brief usage summary.
.TP
\fB-H\fR
Read the signal files in high-resolution mode (default: standard mode).
These modes are identical for ordinary records.  For multifrequency records,
the standard decimation of oversampled signals to the frame rate is suppressed
in high-resolution mode (rather, all other signals are resampled at the highest
sampling frequency).
.TP
\fB-j\fR
Find and annotate J-points (QRS ends) as well as QRS onsets.
.TP
\fB-m\fR \fIthreshold\fR
Specify the detection \fIthreshold\fR (default: 100 microvolts);  use higher
values to reduce false detections, or lower values to reduce the number of
missed beats.
.TP
\fB-p\fR \fIfrequency\fR
Specify the power line (mains) frequency used at the time of the recording,
in Hz (default: 60).  \fBwqrs\fR will apply a notch filter of the specified
frequency to the input signal before length-transforming it.
.TP
\fB-R\fR
Resample the input at 120 Hz if the power line frequency is 60 Hz, or at
150 Hz otherwise (default: do not resample).
.TP
\fB-s\fR \fIsignal\fR
Specify the \fIsignal\fR (number or name) to be used for QRS detection
(default: 0).
.TP
\fB-t\fR \fItime\fR
Process until the specified \fItime\fR in \fIrecord\fR (default: the end of the
\fIrecord\fR).
.TP
\fB-v\fR
Verbose mode: print information about the detector parameters.
.SH ENVIRONMENT
.PP
It may be necessary to set and export the shell variable \fBWFDB\fR (see
\fBsetwfdb\fR(1)).
.SH EXAMPLES
.PP
To mark QRS complexes in record 100 beginning 5 minutes from the start, ending
10 minutes and 35 seconds from the start, and using signal 1, use the command:
.br
	\fBwqrs -r 100 -f 5:0 -t 10:35 -s 1\fR
.br
The output annotations may be read using (for example):
.br
	\fBrdann -a wqrs -r 100\fR
.PP
To evaluate the performance of this program, run it on the entire record, by:
.br
	\fBwqrs -r 100\fR
.br
and then compare its output with the reference annotations by:
.br
	\fBbxb -r 100 -a atr wqrs\fR
.SH SEE ALSO
\fBbxb\fR(1), \fBecgpuwave\fR(1), \fBrdann\fR(1), \fBsetwfdb\fR(1),
\fBsqrs\fR(1)
.PP
Zong W, Moody GB, and Jiang D.
A robust open-source algorithm to detect onset and duration of QRS
complexes.
\fIComputers in Cardiology\fR \fB30\fR:737\-740 (2003).
.SH AUTHORS
Wei Zong (wzong@mit.edu) and George B. Moody (george@mit.edu).
.SH SOURCE
http://www.physionet.org/physiotools/wfdb/app/wqrs.c
